iOS实现左右拖动抽屉效果

#import "DarwViewController.h"
@interface DarwViewController ()
@property (nonatomic, weak) UIView *leftView;
@property (nonatomic, weak) UIView *rightView;
@property (nonatomic, weak) UIView *mainView;
/**
 * 动画是否进行
 */
@property (nonatomic ,assign) BOOL animating;
 
@end
 
@implementation DarwViewController
- (void)viewDidLoad {
 [super viewDidLoad];
}
 
 
-(void)loadView
{
 self.view = [[UIView alloc]initWithFrame:[UIScreen mainScreen].bounds];
 //左边view
 UIView *leftView = [[UIView alloc]initWithFrame:self.view.frame];
 [self.view addSubview:leftView];
 leftView.backgroundColor= [UIColor redColor];
 self.leftView = leftView;
  
 //右边View
 UIView *rightView = [[UIView alloc]initWithFrame:self.view.frame];
 [self.view addSubview:rightView];
 rightView.backgroundColor= [UIColor blueColor];
 self.rightView = rightView;
  
 //主页面
 UIView *mainView = [[UIView alloc]initWithFrame:self.view.frame];
 [self.view addSubview:mainView];
 mainView.backgroundColor= [UIColor yellowColor];
 self.mainView = mainView;
  
  
 //KVO监听
 [self.mainView addObserver:self forKeyPath:@"frame" options:NSKeyValueObservingOptionNew context:nil];
}
/**
 * KVO回调方法 当mainView Frame值改变时触发
 *
 * @param keyPath <#keyPath description#>
 * @param object <#object description#>
 * @param change <#change description#>
 * @param context <#context description#>
 */
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
 if (self.animating) return; //如果mainView正在动画 就不执行
 if (self.mainView.frame.origin.x > 0 )
 {
  //X > 0 就隐藏右边View 显示左边View
  self.rightView.hidden = YES;
  self.leftView.hidden = NO;
 }
 else if (self.mainView.frame.origin.x < 0)
 {
  //X < 0 就隐藏左边View 显示右边VIew
  self.leftView.hidden = YES;
  self.rightView.hidden = NO;
 }
}
#pragma mark -- 触摸事件
-(void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
 //获得触摸对象
 UITouch *touch = [touches anyObject];
  
 //获得当前触摸点
 CGPoint currentPoint = [touch locationInView:self.view];
 //获得上一个触摸点
 CGPoint previousPoint = [touch previousLocationInView:self.view];
  
 //计算x方向的偏移量
 CGFloat offsetX = currentPoint.x - previousPoint.x;
// 根据x的偏移量计算y的偏移量
 self.mainView.frame = [self rectWithOffsetX:offsetX];
  
}
#define screenW [UIScreen mainScreen].bounds.size.width
#define screenH [UIScreen mainScreen].bounds.size.height
/**
 * 计算主视图的frame
 *
 * @param offsetX x的偏移量
 *
 * @return 偏移后新的frame
 */
- (CGRect ) rectWithOffsetX:(CGFloat )offsetX
{
 //Y轴的偏移量
 CGFloat offsetY = (screenH *1/5) * (offsetX/screenW);
  
 //比例 ：（用于宽高的缩放）
 CGFloat scale = (screenH - offsetY *2) / screenH;
 if (self.mainView.frame.origin.x < 0 )
 {
  //如果x是负数 及左边View要显示
  //比例就要设为比1小
  scale = 2 - scale;
 }
 //获取当前mainView的frame
 CGRect frame = self.mainView.frame;
  
 //重新设置mainView的frame值
 frame.size.width = frame.size.width *scale >screenW ? screenW : frame.size.width *scale;
  
 frame.size.height = frame.size.height *scale >screenH ? screenH :frame.size.height *scale;
  
 frame.origin.x += offsetX;
 frame.origin.y =(screenH - frame.size.height)*0.5;
 //返回偏移后新的frame
 return frame;
}
#define maxRightX (screenW *0.8)
#define maxLeftX (-screenW *0.6)
-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
 CGFloat targetX = 0;
 //如果松手的那一下 当前mainVIew的x大于屏幕的一半
 if (self.mainView.frame.origin.x > screenW * 0.5)
 {
  //向右边定位
  targetX = maxRightX;
 }
 //如果松手的那一下 当前mainVIew的最大X值小于屏幕的一半
 else if (CGRectGetMaxX(self.mainView.frame) < screenW *0.5)
 {
  //向左边定位
  targetX = maxLeftX;
 }
  
 //计算偏移量
 CGFloat offsetX = targetX -self.mainView.frame.origin.x;
  
 self.animating = YES;
  
 [UIView animateWithDuration:0.4 animations:^{
  if (targetX == 0)
  {
   //如果targetX==0 复位
   self.mainView.frame = self.view.frame;
  }
  else
  {
   //如果targetX != 0 那就到指定位置
   self.mainView.frame = [self rectWithOffsetX:offsetX];
  }
 } completion:^(BOOL finished) {
  self.animating = NO;
 }];
   
}
@end